With the rapid development of laser technology and the increasing application demand thereof, the tendency of laser field is to realize the high-power, high beam quality, high efficiency, high stability and long life of a laser device which is in small size, compact structure, stable performance, and all solid state. In a variety of technical fields and industries, the demand for ultra short pulse laser is increasingly higher, especially for the picosecond laser, which has more application prospect than a femtosecond laser (for example, the fields of the national defense, industrial, medical, biological, and other areas). Therefore, a current important research task is to develop a high-quality, high efficiency, high stability picosecond laser.
According to one existing picosecond laser technology, a dye mode-locked, is utilized, for example, a published Chinese patent application No. 03114621.X, entitled as “high light-output time stability passive mode-locked Nd:YAG picosecond laser device” which has complex and bulky electronic control system. Also, the dye, being of highly toxic, would be diluted after some time, so needs to be replaced, therefore the life time is short which is not facilitated for industrialization and human health. According to another existing mode-locked picosecond laser device technology, active mode-locked technology is utilized, such as, the Chinese patent application No. 03210775.7, entitled as “laser-diode-pump picosecond active mode-locked solid planar waveguide laser device”. Because the technology of wave-guide is developed prematurely and the yield is very low, it is difficult to produce mode-locked picosecond laser device in large scale, and such active mode-locked has low stability performance. There is another existing mode-locked picosecond laser device technology, a passive mode-locked technology used for realizing low-repetition-frequency, such as Chinese utility model application No. 200520000394.7, entitled as “cavity-dumped all-solid-state picosecond laser device”, wherein Pockels cell is used to realize cavity-dumped giant laser pulse oscillations, which significantly damages the SESAM, and such damage can not be restored once occurring.
In addition, confocal structure is popularly used in the laser cavity of the existing laser device technology. Although such structure is stable, the cavity is relatively longer with the structure incompact.
To sum up, the existing technologies are lack of a low-repetition-frequency passive mode-locked picosecond laser with compact structure and stable performance.